Is Marijuana Addictive?

Does marijuana cause addiction? As Californians prepare to vote on Prop 19 — which would legalize recreational use of the drug, at least under state law — the question is more pertinent than ever. The answer, however, is less than clear: addiction experts tend to agree that pot is addictive, but nonspecialists and much of the public see it differently. It all depends on what you mean by "addiction."

The definition most commonly accepted by addiction experts is a boiled-down version of the one laid out in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV TR), psychiatry's handbook of all mental conditions. By the book, addiction is the compulsive use of a substance despite ongoing negative consequences, which may lead to tolerance or withdrawal symptoms when the substance is stopped. By this definition, about 10% of people who smoke marijuana become addicted to it. (More on Time.com: PHOTOS — Cannabis Conventions).

However, nonspecialists (including many doctors) still tend to use an older perspective, now seen as outdated by experts. From their point of view, some drugs may be considered physically addictive — producing severe withdrawal — while others are psychologically addictive and only cause craving; those that are both are the hardest to quit.

Former Surgeon General Jocelyn Elders characterized marijuana succinctly on CNN recently, while declaring her support for legalization: "Marijuana is not addictive, not physically addictive anyway."

In this view, the paradigm for addiction is heroin: the shaking, puking heroin junkie who can't quit because the withdrawal sickness is impossible to bear. Because marijuana cessation is not linked with such severe symptoms, the drug isn't seen as physically addictive. And considering that most people view physical addiction as uncontrollable, but psychological addiction as manageable with proper willpower, marijuana tends not to be regarded as addictive in general. (More on Time.com: Addiction Files: Recovering From Drug Addiction, Without Abstinence).

But virtually all addiction experts disagree with that stance. "The distinction is completely arbitrary. Psychological addiction occurs in your brain and it's a physical change," says Dr. Nora Volkow, director of the National Institute on Drug Abuse. Different brain processes may be involved in the psychological drive to take drugs and in the physical withdrawal symptoms when the drug is stopped — but both are brain changes.

As it turns out, the psychological drive is much more powerful than the physical experience of withdrawal. Cocaine, which also produces little withdrawal sickness but does create extreme craving, was once seen as nonaddictive — that was before America was introduced to crack in the 1980s. More than a century ago, Mark Twain summed up the essence of the problem, in reference to the addictiveness of tobacco: "Giving up smoking is easy," he said. "I've done it thousands of times."

I personally had the same experience with heroin. I got through the nausea and chills at least five different times, but avoiding the psychological draw of the drug long-term was much harder than suffering through a few weeks of withdrawal symptoms. Quitting cocaine is similar. (More on Time.com: Best of 'Stoner Cinema').

So the question is, how does marijuana compare to these classically addictive drugs? Estimates vary, but compared with tobacco, which hooks about 20% to 30% of smokers, marijuana is much less addictive, coming in at 9% to 10%. In contrast, 23% to 25% of heroin users get addicted, along with 15% of alcohol users and 15% to 20% of those who use cocaine.

Marijuana is the most heavily used drug in the country — by their 20s, 56% of Americans have tried it — but only 16% of people who are in addiction treatment report that marijuana is their primary drug. In contrast, just 2% of young adults have ever tried heroin, but heroin addicts make up 14% of treatment admissions.

Overall, then, addiction rates for marijuana are significantly lower than for other drugs, both legal and illegal. What about withdrawal symptoms? "You see mood effects, irritability. Food intake decreases. There are sleep disruptions. It looks like nicotine withdrawal," says Carl Hart, assistant professor of clinical neuroscience at Columbia University, who has studied marijuana withdrawal. "You can actually die from alcohol withdrawal. Heroin withdrawal you can't really die from; it's more like the flu. Marijuana withdrawal is annoying, but it isn't life threatening." (Full disclosure: Hart and I are currently collaborating on a new book.)

According to Stanton Peele, author of the classic book Love and Addiction, the real question is not the substance's addictive quality, but its potential for harm. "I wrote an article on this titled 'Marijuana is addictive — so what?'" he says. "How harmful is this addiction compared to other addictions? It can be disruptive to people's lives; I have a treatment center, and some people end up there because of marijuana. On the other hand, in terms of physical assaults to your body, it's better than smoking and better than alcohol." (More on Time.com: The Marijuana Number That Was Too Good to Check)

As Dr. Elders also said on CNN, marijuana is nontoxic. You can fatally overdose on alcohol, heroin or cocaine, but the only way a dose of marijuana will kill you is if someone crushes you under a bale of it.

In fact it may be the social consequences of using marijuana that are more harmful than the physical ones. Peele notes that being convicted for marijuana possession can make a college student ineligible for federal student aid. "No psychologist in the universe could possibly say that smoking marijuana is worse for you than being deprived of the opportunity to get an education," says Peele.

Hart agrees. "I've studied the effects of marijuana withdrawal and effects on cognition. I was ambivalent about it for a long time," he says. "I now have a 15-year-old son. I am far more concerned about him interacting with law enforcement than I am with marijuana, based on the research." (More on Time.com: Is Drug Use Really on the Rise?).

And the debate over new ways to regulate addictive substances may only just be beginning. The forthcoming fifth edition of the DSM will include gambling addiction as well as drug addictions under the broader category of addictions. "We are recognizing that addiction is broader than we thought. It's not just the concept of some heroin addict living in a cardboard box on the street," says Peele. Anything that is absorbing and pleasurable — from the Internet to sex, pornography, food, shopping and even, for some people, eating carrots — can be considered addictive in this view. It may be impossible for regulators to keep up.

Pot may be habit forming, but it is not addictive. People who burn all the time can put down the bowl long enough to clean up to piss for a potential job. If it were truly addictive, you'd hear stories all the time about how marijuana ruined someone's life. (like meth or heroin use)